Universal terminal bar structure with ground contacting feature integrated into a body structure with versatile RFI suppression for electric motors

ABSTRACT

A method of providing RFI suppression in a DC motor provides a universal terminal bar structure  70  including a positive terminal bar  72  and a negative terminal bar  76 , a first choke  80  electrically connected with the positive terminal bar, a second choke  82  electrically connected with the negative terminal bar, a first ground connection  86  constructed and arranged to electrically connect the positive terminal bar to ground, a first breakable section A between the first ground connection and the positive terminal bar, a second ground connection  88  constructed and arranged to electrically connect the negative terminal bar to ground, and a second breakable section B between the second ground connection and the negative terminal bar. Capacitor structure  90  is attached to the terminal bar structure, and the first breakable section is selectively broken, alone or in combination with the second breakable section to provide versatile RFI suppression.

This application is based on U.S. Provisional Application No.60/550,474, filed on Mar. 5, 2004 and claims the benefit thereof forpriority purposes.

FIELD OF THE INVENTION

The invention relates to permanent magnet direct current (DC) motors forautomotive applications and, more particular, to a terminal barstructure that provides versatile RFI suppression.

BACKGROUND OF THE INVENTION

The functionality of permanent magnet direct current brush-commutatedelectric motors requires switching current from winding to winding. Asthe brushes slide from one bar to another an arching occurs due to theback electromotive force (EMF) generated by the stored electromagneticenergy in the current carrying coils. The arching generates broadbandelectrical noise over a wide frequency spectrum. The spectrum energydistribution is influenced by switching of coils (commutation) that isproportional to the motor speed.

There are two modes of conducted noise generated in a motor,differential mode and common mode. The differential mode filtering canbe accomplished with a shunt capacitor connected across the positive andnegative motor terminals and use of series inductors or ferrite beads(chokes) to reduce radio frequency (RF) noise currents. The common modefiltering is also accomplished by including series impedance in bothleads in addition to referencing the shunt capacitor and the negativeterminal to case. However, the motor case and vehicle ground must be atthe same potential. If the case and vehicle ground are at differentpotential then the RF reference can be provided by an additionalcapacitor. This type of filtering is shown in FIGS. 1, 2, and 3.

FIG. 1 shows a conventional brush card assembly 10 for a two brush, fourpole (permanent magnet) motor with a link wound commutator. In thiscase, the Radio Frequency Interference (RFI) filtering is realized byplacing a capacitor 11 between the positive terminal bar 12 and negativeterminal bar 14 that are directly connected to the respective chokes.The positive choke 16 is connected to the positive brush inside brushtube 18 via a shunt wire 20 and the negative choke n22 is connected tothe negative brush inside brush tube 24 via shunt wire 26. Furthermore,a motor case/stator assembly is connected to the negative terminal bar14 through the ground shunt wire 28. The ground shunt wire 28 is at thesame potential as the vehicle ground. In this case, the terminal barsare insert molded into a connector body 30.

FIG. 2 shows a conventional brush card assembly 10′ for a two brush,four pole (permanent magnet) motor with a link wound commutator. In thiscase, RFI filtering is realized by placing a capacitor 32 between thepositive terminal bar 16 and motor case/stator assembly and anothercapacitor 34 between the negative terminal bar 14 and the motorcase/stator assembly. Therefore, the motor case has the same potentialas the vehicle ground. The terminal bars are directly connected to therespective chokes (the positive choke 16 is connected to the positivebrush 18 and the negative choke 22 is connected to the negative brush 24in the manner discussed above with regard to FIG. 1). In this case, thepositive lead wire 36 and the negative lead wire 38 are attached to theterminal bars and the assembly is then over molded in a grommet 40.

FIG. 3 a shows a conventional brush card assembly for a four brush, fourpole (permanent magnet) motor. In this case, the RFI filtering is a bitmore complex because there are four brushes used (two positive 18, 18′and two negative 24, 24′) and there is a choke 37 connected between eachbrush and the respective power input terminal bar. As shown in FIG. 3 b,two chokes are not seen since they are on the other side of the brushcard. The capacitor 42 is connected between the positive terminal inputbar 44 and the negative input terminal bar 46. The capacitor 48 isconnected between the positive input terminal bar 44 and motorcase/stator assembly. Also, the motor case/stator assembly has the samepotential as the vehicle ground through the ground shunt wire 50. Inthis case, similar to the brush card in FIG. 2, the lead wires 36, 38are attached to the terminal bars and the assembly is then over moldedin a grommet.

FIG. 4 shows another conventional brush card assembly with four brushesfor a four pole (permanent magnet) motor. However there are only twochokes used, one for both positive brushes and the other one for bothnegative brushes. The choke 52 is connected between the negative inputterminal bar 46 and the brush 54 (negative brush). The choke 56 isconnected between the positive input power terminal bar 44 and brush 58(positive brush). The capacitor 60 is connected between the positive andnegative input terminal bars. The capacitor 62 is connected between thepositive input terminal bar and motor case/stator assembly. In thiscase, the negative terminal bar 46 has an extended feature 64 (insteadof the ground shunt wire as shown in FIGS. 1, 2, and 3)) to make contactto the motor case/stator assembly. Therefore, the motor case/statorassembly still has the same polarity as the vehicle ground.

Although the construction of the brush card assembly for a four-brushconfiguration is significantly different from the two-brushconfiguration, the method of assembling the capacitors and grounding tomotor case for RFI suppression are the same. The attachment ofcapacitors 32, 48, and 62 in FIGS. 2, 3 and 4, respectively, andcapacitor 34 in FIG. 2 is manual labor intensive. Furthermore, paintmust be removed (grinded off) from the stator/motor case at the contactarea of ground strap shunt wire or the ground terminal bar in order toensure proper grounding.

Therefore, a more universal and versatile terminal bar system is neededthat can be more cost effective and that can accommodate automatedassembly.

SUMMARY OF THE INVENTION

An object of the invention is to fulfill the need referred to above. Inaccordance with the principles of the present invention, this objectiveis achieved by a method of providing RFI suppression in a DC motor. Themethod provides a universal terminal bar structure including a positiveterminal bar and a negative terminal bar, a first ground connectionconstructed and arranged to electrically connect the positive terminalbar to ground, a first breakable section between the first groundconnection and the positive terminal bar, a second ground connectionconstructed and arranged to electrically connect the negative terminalbar to ground, and a second breakable section between the second groundconnection and the negative terminal bar. Capacitor structure isattached to the terminal bar structure, and the first breakable sectionis selectively broken, alone or in combination with the second breakablesection to provide versatile RFI suppression.

In accordance with another aspect of the invention, a universal terminalbar structure is provided for a permanent magnet DC motor. The structureincludes a body structure, a positive terminal bar and a negativeterminal bar, each being carried by the body structure, a first groundconnection constructed and arranged to electrically connect the positiveterminal bar to ground, a first breakable section between the firstground connection and the positive terminal bar constructed and arrangedsuch that when the first breakable section is broken, the connectionbetween ground and the positive terminal bar is terminated, a secondground connection constructed and arranged to electrically connect thenegative terminal bar to ground, a second breakable section between thesecond ground connection and the negative terminal bar constructed andarranged such that when the second breakable section is broken, theconnection between ground and the negative terminal bar is terminated,and capacitor structure attached to the terminal bar structure. Wherebyplacement of the capacitor structure and selectively breaking the firstbreakable section, alone or in combination with the second breakablesection, provides selective radio frequency interference (RFI)suppression for the motor.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings, wherein like reference numerals refer tolike parts, in which:

FIG. 1 shows a conventional brush card assembly for a two brush,four-pole permanent magnet motor with terminal bars molded into aconnector body.

FIG. 2 shows a conventional brush card assembly for a two brush,four-pole permanent magnet motor with lead wires attached to theterminal bars when molded in a grommet.

FIG. 3 a shows a top side of a conventional brush card assembly for afour brush, four-pole permanent magnet motor with four chokes and withlead wires attached to the terminal bars when molded in a grommet.

FIG. 3 b show a bottom side of the brush card assembly of FIG. 3 a.

FIG. 4 shows a conventional brush card assembly for a four brush,four-pole permanent magnet motor having two chokes with a negativeterminal bar having an extended feature to contact a motor case/statorassembly.

FIG. 5 is a schematic illustration of a terminal bar structure providedin accordance with the principles of the present invention.

FIG. 6 is a partial sectional view of a ground connection of theinvention being compressed between an end cap and the motor case/statorassembly.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

With reference to FIG. 5, a terminal bar structure, generally indicatedat 70, is shown in accordance with the invention. The terminal barstructure has a positive terminal bar 71, of a generally Y-shapedefining a high-speed connection branch 72 and a medium speed connectionbranch 74 joined at a common member 75. The terminal bar structure 70also includes a negative terminal bar 76. The terminal bar structure 70can be cut-out/stamped-out on a progressive die as one piece or twopieces (the positive bar separate from the negative bar) or evenmultiple pieces. This depends on the construction and complexity of amolding die that is used for molding a grommet 78 or connector bodystructure around the terminal bar structure 70. If the terminal barstructure 70 is made as one piece, the positive terminal bar 71 must beseparated from the negative terminal bar 76.

A break-off (breakable) section encircled at A in FIG. 5 is provided onthe positive terminal bar 71 and a break-off (breakable) sectionencircled at B in FIG. 5 is provided on the negative terminal bar 76.These break-off sections can be selectively cut-off depending on thetype of RFI suppression being used, as will be apparent below. In theillustrated embodiment, at least one choke 80 is attached to the commonmember 75 of the positive terminal bar 71 and at least one choke 82 isattached to the negative terminal bar 76. The chokes are directlyattached to the respective polarity brushes (the brushes are not shownin FIG. 5). Additional chokes can be attached in series or in parallelto the positive terminal bar and negative terminal bar depending on thenumber of brushes used, or the level of RFI suppression required. If nochokes are provided, the positive brush can be connected directly to thepositive terminal bar 71 and the negative brush can be connecteddirectly to the negative terminal bar 76.

With the terminal bar structure 70, the following type of RFIsuppressions can be achieved:

1. The Type 1 RFI suppression as shown in FIG. 1 can be achieved withthe terminal bar structure 71 by attaching only capacitor 84 between thepositive terminal bar 71 and negative terminal bar 76 as shown in FIG.5. Furthermore, the break-off section A is removed/cut to break thecontact of the positive terminal bar to motor case/stator assemblythrough the ground connection portion 86 of the positive terminal bar71. However, the break-off section B remains part of the negativeterminal bar 76; therefore, the motor case/stator assembly is connectedto the vehicle ground through the ground connection portion 88 of thenegative terminal bar 76.

2. The Type 2 RFI suppression as shown in FIG. 2 can be achieved withthe terminal bar structure 70 by attaching capacitor 90 and capacitor 92(but not capacitor 84) to the terminal bar structure 70 as shown in FIG.5. Thus, capacitor 90 is electrically connected between the groundconnection 86 and the positive terminal bar 71 and capacitor 92 iselectrically connected between the ground connection 88 and the negativeterminal bar 76. Furthermore, both break-off section A and break-offsection B are removed/cut to eliminate direct contact of terminal bars71 and 76 to motor case/stator assembly.

3. The Type 3 RFI suppression as illustrated on FIG. 3 and FIG. 4 can beachieved with the terminal bar structure 70 by attaching capacitor 90and capacitor 84 (but not capacitor 92) to the terminal bar structure 70as shown in FIG. 5. Thus, capacitor 90 is electrically connected betweenthe ground connection 86 and the positive terminal bar 71 and capacitor84 is electrically connected between the positive terminal bar 71 andthe negative terminal bar 76. Furthermore, the break-off section A isremoved/cut to break the contact of the positive terminal bar to motorcase/stator assembly through the ground connection 86 of the positiveterminal bar 71. However, the break-off section B remains part of thenegative terminal bar 76; therefore, the motor case/stator assembly isconnected to the vehicle ground through the ground connection 88 of thenegative terminal bar 76.

Thus, breakable section A is always cut, broken or removed, andbreakable section B is cut or broken only when capacitor 92 is employed.Providing the breakable sections A and B enables the terminal bars 72and 76 to be cut out or stamped as explained above.

The capacitors are assembled, for example, by resistance welding/fusingor ultrasonic welding (however the assembly is not limited to thesemethods). The grommet or connector body 78 can be molded after or beforethe capacitors are assembled to the terminal bar structure 70. However,the positive lead wire 38 and the negative lead wire 36 need to beattached to the associated terminal bar before molding the grommet 78around the terminal bars.

The advantage with the versatile terminal bar structure 70 is that theattachment of capacitor and ground connections can be automated. Also,the capacitors are placed on the terminal bar structure 70 based on thetype and level of RFI suppression requirements. Therefore, with thisstructure, multiple type and levels of RFI suppression can be achieved.

Also, the same grommet or connector body structure 78 with the insertmolded terminal bars can be used for one or two or even three positivepower input applications. This requirement is quite common when one ortwo resistors are connected in series to the motor for two or threespeed application. The advantage of this structure is that with the“flow through” feature 94 on the positive terminal bar 71 all positivepower inputs are jointed and insert molded into the grommet or connectorbody 78.

Another advantage of the terminal bar structure 70 is the method ofgrounding to the motor case/stator assembly. This is illustrated in FIG.6, where the ground connection 80, 88 of the terminal bar structure 70is compressed between an end cap 96 of a motor and the motor case/statorassembly 98. Under compressive load the ground connection bar cuts intothe motor case/stator assembly to ensure adequate ground connection.

Features of the invention include:

-   1. Integrate ground contact terminal bar into grommet or connector    body structure.-   2. Insert mold RFI suppression components into grommet or connector    body structure.-   3. Integrate FRI suppression component into grommet or connector    body structure.-   4. Insert mold terminal bar to grommet or connector body structure    with flow through feature to accommodate for two or multiple    terminal power inputs but with only two terminals to the RFI chokes    or brushes.-   5. A method of ground connection without grinding paint from the    motor case/stator assembly.-   6. Insert molded terminal bar with features such as the break-off    sections that allow for a versatile RFI suppression assembly.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

1-10. (canceled)
 11. A method of providing RFI suppression in a DC motorincluding: providing a universal terminal bar structure comprising: apositive terminal bar and a negative terminal bar, a first groundconnection constructed and arranged to electrically connect the positiveterminal bar to ground, a first breakable section between the firstground connection and the positive terminal bar, a second groundconnection constructed and arranged to electrically connect the negativeterminal bar to ground, and a second breakable section between thesecond ground connection and the negative terminal bar, attachingcapacitor structure to the terminal bar structure, and selectivelybreaking the first breakable section alone or in combination with thesecond breakable section.
 12. The method of claim 11, wherein the stepof attaching capacitor structure includes electrically connecting acapacitor between the positive terminal bar and the negative terminalbar.
 13. The method of claim 12, wherein the step of breaking includesbreaking only the first breakable section so as to terminate theconnection between ground and the positive terminal bar is terminated.14. The method of claim 11, wherein the step of attaching capacitorstructure includes electrically connecting a capacitor between the firstground connection and the positive terminal bar and electricallyconnecting another capacitor between the positive terminal bar and thenegative terminal bar.
 15. The method of claim 14, wherein the step ofbreaking includes breaking only the first breakable section so as toterminate the connection between ground and the positive terminal bar isterminated.
 16. The method of claim 11, wherein the step of attachingcapacitor structure includes electrically connecting a capacitor betweenthe first ground connection and the positive terminal bar andelectrically connecting another capacitor between the second groundconnection and the negative terminal bar.
 17. The method of claim 16,wherein the step of breaking includes breaking both the first breakablesection and the second breakable section to eliminate direct contact ofthe terminal bars to ground.
 18. The method of claim 11, furtherincluding molding a connector body about at least a portion of theterminal bar structure.
 19. The method of claim 11, further includingattaching a lead wire to the positive terminal bar and attaching anotherlead wire to the negative terminal bar and thereafter, molding aconnector body about at least a portion of the terminal bar structure.20. The method of claim 11, further including electrically connecting atleast one first choke with the positive terminal bar and electricallyconnecting at least one second choke with the negative terminal bar. 21.The method of claim 11, wherein the motor includes an end cap and amotor case, the method further including compressing the first andsecond ground connections between the end cap and motor case such thatunder compression, the ground connections cut into the motor case tocreate ground contact.
 22. The method of claim 11, wherein the step ofproviding the terminal bar structure includes providing the terminal barstructure as a single piece and then separating the positive terminalbar from the negative terminal bar.